A hammer tool disclosed in Japanese Unexamined Patent Application Publication No. 2002-79476, drives a striker via an air pressure fluctuation within an air chamber or an air spring effect caused by relative movement between a piston as a driving element and the striker as a hammering element, and the driven striker moves forward and hits a hammer bit.
In the hammer tool described above, when a hammering operation while pushing a tip of the hammer bit against a workpiece, a stroke amount of the piston is varied in accordance with pushing force that a user applies to a grip of the hammer tool. Thereby, the hammer tool controls impact force during the hammering operation.